Positive resist composition, monomer, polymer, and patterning process

ABSTRACT

A positive resist composition is provided comprising a polymer comprising recurring styrene units having an ester group bonded to a CF 3 —C(OH)—R 3  group (R 3 ═H, CH 3 , or CF 3 ) such as 1,1,1,3,3,3-hexafluoro-2-propanol and having a Mw of 1,000-500,000. The resist composition has a satisfactory effect of suppressing acid diffusion and a high resolution, and forms a pattern of good profile and minimal edge roughness after exposure.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a)on Patent Application No. 2012-271260 filed in Japan on Dec. 12, 2012,the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a positive resist composition, and moreparticularly to a chemically amplified positive resist composition; anda patterning process using the same. It also relates to a monomer and apolymer for use in the resist composition as base resin.

BACKGROUND ART

To meet the demand for higher integration density and operating speed ofLSIs, the effort to reduce the pattern rule is in rapid progress. Thewide-spreading flash memory market and the demand for increased storagecapacities drive forward the miniaturization technology. As the advancedminiaturization technology, manufacturing of microelectronic devices atthe 65-nm node by the ArF lithography has been implemented in a massscale. Manufacturing of 45-nm node devices by the next generation ArFimmersion lithography is approaching to the verge of high-volumeapplication. The candidates for the next generation 32-nm node includeultra-high NA lens immersion lithography using a liquid having a higherrefractive index than water in combination with a high refractive indexlens and a high refractive index resist film, extreme ultraviolet (EUV)lithography of wavelength 13.5 nm, and double patterning version of theArF lithography, on which active research efforts have been made.

With respect to high-energy radiation of very short wavelength such aselectron beam (EB) or x-ray, hydrocarbons and similar light elementsused in resist materials have little absorption. Then polyhydroxystyrenebase resist materials are under consideration.

The exposure system for mask manufacturing made a transition from thelaser beam exposure system to the EB exposure system to increase theaccuracy of line width. Since a further size reduction becomes possibleby increasing the accelerating voltage of the electron gun in the EBexposure system, the accelerating voltage increased from 10 kV to 30 kVand reached 50 kV in the current mainstream system, with a voltage of100 kV being under investigation.

As the accelerating voltage increases, a lowering of sensitivity ofresist film becomes of concern. As the accelerating voltage increases,the influence of forward scattering in a resist film becomes so reducedthat the contrast of electron image writing energy is improved toameliorate resolution and dimensional control whereas electrons can passstraightforward through the resist film so that the resist film becomesless sensitive. Since the mask exposure tool is designed for exposure bydirect continuous writing, a lowering of sensitivity of resist filmleads to an undesirably reduced throughput. Due to a need for highersensitivity, chemically amplified resist compositions are contemplated.

As the feature size reduces, image blurs due to acid diffusion become aproblem. To insure resolution for fine patterns with a size of 45 nm etseq., not only an improvement in dissolution contrast is important aspreviously reported, but control of acid diffusion is also important asreported in SPIE Vol. 6520 65203L-1 (2007). Since chemically amplifiedresist compositions are designed such that sensitivity and contrast areenhanced by acid diffusion, an attempt to minimize acid diffusion byreducing the temperature and/or time of post-exposure bake (PEB) fails,resulting in drastic reductions of sensitivity and contrast.

A triangular tradeoff relationship among sensitivity, resolution, andedge roughness has been pointed out. Specifically, a resolutionimprovement requires to suppress acid diffusion whereas a short aciddiffusion distance leads to a loss of sensitivity.

The addition of an acid generator capable of generating a bulky acid isan effective means for suppressing acid diffusion. It was then proposedto incorporate in a polymer an acid generator of an onium salt having apolymerizable olefin. JP-A 2006-045311 discloses a sulfonium salt havingpolymerizable olefin capable of generating a specific sulfonic acid anda similar iodonium salt. JP-A 2006-178317 discloses a sulfonium salthaving sulfonic acid directly attached to the main chain.

A tradeoff relationship between sensitivity and edge roughness has beenpointed out. For example, SPIE Vol. 3331 p 531 (1998) describes thatsensitivity is in inverse proportion to edge roughness. It is expectedthat the edge roughness of a resist film is reduced by increasing theexposure dose to reduce shot noise. SPIE Vol. 5374 p 74 (2004) describesa tradeoff between sensitivity and roughness in the EUV lithography inthat a resist material containing a more amount of quencher is effectivein reducing roughness, but suffers from a decline of sensitivity at thesame time. There is a need to enhance the quantum efficiency of acidgeneration in order to overcome the problem.

With respect to the acid generating mechanism triggered by EB exposure,SPIE Vol. 5753 p 361 (2005) reports that PAG releases acid through themechanism that a polymer is excited by exposure so that electronsmigrate to the PAG. Since the irradiation energy of EB or EUV is higherthan the threshold value (10 eV) of ionization potential energy of abase polymer, it is presumed that the base polymer is readily ionized.An exemplary material of accelerating electron migration ishydroxystyrene.

It is reported in SPIE Vol. 5753 p 1034 (2005) thatpoly-4-hydroxystyrene has a higher acid generation efficiency in EBexposure than poly-4-methoxystyrene, indicating thatpoly-4-hydroxystyrene provides for efficient migration of electrons toPAG upon EB exposure.

Reported in SPIE Vol. 6519 p 65191F-1 (2007) is a material obtainedthrough copolymerization of hydroxystyrene for increasing the acidgeneration efficiency by electron migration, a methacrylate of PAGhaving sulfonic acid directly bonded to a polymer backbone forsuppressing acid diffusion, and a methacrylate having an acid labilegroup. Since hydroxystyrene has a phenolic hydroxyl group which isweakly acidic, it is effective for reducing swell in alkaline developer,but causes to increase acid diffusion. On the other hand, a methacrylatehaving lactone as the adhesive group is widely employed in the ArFresist composition. Since this methacrylate has high hydrophilicity andno alkaline solubility, it is ineffective for reducing swell, buteffective for suppressing acid diffusion. A combination ofhydroxystyrene and lactone-containing methacrylate as the adhesive groupcan establish a fairly good balance among sensitivity improvement, swellreduction, and acid diffusion control, but is still insufficient.

An attempt is made to improve the sensitivity of a resist material byusing a component which is highly absorptive to EUV. Fluorine is atypical element which is highly absorptive to EUV. Resist polymershaving pentafluorostyrene or 1,1,1,3,3,3-hexafluoro-2-propanolstyrenecopolymerized therein are under study. Despite improved sensitivity,these polymers still suffer from the problems of increased aciddiffusion, reduced alkaline solubility, and degraded resolution. Itwould be desirable to have a resist material having higher sensitivityand resolution.

CITATION LIST

-   Patent Document 1: JP-A 2006-045311 (U.S. Pat. No. 7,482,108)-   Patent Document 2: JP-A 2006-178317-   Non-Patent Document 1: SPIE Vol. 6520 65203L-1 (2007)-   Non-Patent Document 2: SPIE Vol. 3331 p 531 (1998)-   Non-Patent Document 3: SPIE Vol. 5374 p 74 (2004)-   Non-Patent Document 4: SPIE Vol. 5753 p 361 (2005)-   Non-Patent Document 5: SPIE Vol. 5753 p 1034 (2005)-   Non-Patent Document 6: SPIE Vol. 6519 p 65191F-1 (2007)

SUMMARY OF INVENTION

An object of the present invention is to provide a positive resistcomposition, typically chemically amplified positive resist compositioncomprising a specific polymer, which composition exhibits a higherresolution than the prior art positive resist compositions, minimal edgeroughness (LER, LWR), and a high sensitivity, and forms a pattern ofgood profile after exposure; a patterning process using the resistcomposition; a polymerizable monomer; and a polymer thereof for use inthe resist composition as a base resin.

Making extensive investigations in search for a resist material capableof meeting the current requirements including high sensitivity, highresolution, and minimal edge roughness, the inventors have found that apolymer comprising recurring styrene units having an ester group bondedto a CF₃—C(OH)—R³ group (wherein R³═H, CH₃, or CF₃) such as1,1,1,3,3,3-hexafluoro-2-propanol (HFA) is quite effective as a baseresin in a resist composition, typically chemically amplified positiveresist composition. Although the HFA group normally promotes aciddiffusion, the acid diffusion can be suppressed by bonding an estergroup to the HFA group. When a CF₃—C(OH)—R³ group such as HFA is bondedto an ester group, the hydroxy moiety of the CF₃—C(OH)—R³ group isincreased in acidity. The increased acidity ensures a high dissolutioncontrast via deprotection when the hydroxy moiety is substituted with anacid labile group, or suppresses swell in alkaline developer when thehydroxy moiety is not substituted with an acid labile group.

The inventors have found that a polymer obtained from copolymerizationof a recurring unit having a carboxyl group substituted with an acidlabile group for suppressing acid diffusion and improving dissolutioncontrast with a hydroxyphenyl methacrylate substituted with an alkyl oralkoxy group as represented by the general formula (1) below is usefulas a base resin in a positive resist composition, typically chemicallyamplified positive resist composition, and that a resist compositioncomprising the polymer is improved in such properties as a contrast ofalkali dissolution rate before and after exposure, acid diffusionsuppressing effect, resolution, and profile and edge roughness of apattern after exposure, and thus best suited as a micropatterningmaterial for the fabrication of VLSI and photomasks.

The positive resist composition has a satisfactory effect of suppressingacid diffusion and a high resolution, lends itself to the lithographyprocess, and forms a pattern of good profile and minimal edge roughnessafter exposure. Because of these advantages, the composition is readilyimplemented in practice and best suited as a VLSI-forming resistmaterial and mask pattern forming material.

In one aspect, the invention provides a positive resist compositioncomprising a polymer comprising recurring units of the general formula(1) and having a weight average molecular weight of 1,000 to 500,000 asa base resin.

Herein R¹ is a straight or branched C₁-C₄ alkylene group, R² ishydrogen, C₁-C₁₅, acyl group or acid labile group, R³ is hydrogen,methyl or trifluoromethyl, and a is a number in the range: 0<a≦1.0.

Preferably, the polymer comprises recurring units (a) and acid labilegroup-substituted recurring units (b1) and/or (b2) copolymerizedtogether, as represented by the general formula (2).

Herein R¹, R² and R³ are as defined above, R⁴ and R⁶ each are hydrogenor methyl, R⁵ and R⁹ each are an acid labile group, R⁷ is a single bondor a straight or branched C₁-C₆ alkylene group, R⁸ is hydrogen,fluorine, trifluoromethyl, cyano, or straight, branched or cyclic C₁-C₆alkyl group, p is 1 or 2, q is an integer of 0 to 4, Y¹ is a singlebond, a C₁-C₁₂ linking group having an ester radical, ether radical orlactone ring, phenylene group or naphthylene group, Y² is a single bond,—C(═O)—O— or —C(C═O)—NH—, a, b1 and b2 are numbers in the range:0<a<1.0, 0≦b1<1.0, 0≦b2<1.0, 0<b1+b2<1.0, and 0.1≦a+b1+b2≦1.0.

Preferably, the polymer may further comprise recurring units (c) havingan adhesive group selected from among hydroxyl, carboxyl, lactone ring,carbonate, thiocarbonate, carbonyl, cyclic acetal, ether, ester,sulfonic acid ester, cyano, amide, and —O—C(═O)-G- wherein G is sulfuror NH and c is a number in the range: 0<c≦0.9 and 0.2≦a+b1+b2+c≦1.0.

More preferably, the polymer may further comprise recurring units (d) ofat least one type selected from among sulfonium salt units (d1) to (d3)represented by the general formula (3).

Herein R²⁰, R²⁴, and R²⁸ each are hydrogen or methyl, R²¹ is a singlebond, phenylene, —O—R—, or —C(═O)—Y⁰—R—, Y⁰ is oxygen or NH, R is astraight, branched or cyclic C₁-C₆ alkylene group, alkenylene orphenylene group, which may contain a carbonyl, ester, ether or hydroxylradical, R²², R²³, R²⁵, R²⁶, R²⁷, R²⁹, R³⁰, and R³¹ are eachindependently a straight, branched or cyclic C₁-C₁₂ alkyl group whichmay contain a carbonyl, ester or ether radical, or a C₆-C₁₂ aryl, C₇-C₂₀aralkyl, or thiophenyl group, Z⁰ is a single bond, methylene, ethylene,phenylene, fluorophenylene, —O—R³²—, or —C(C═O)—Z¹—R³²—, Z¹ is oxygen orNH, R³² is a straight, branched or cyclic C₁-C₆ alkylene group,alkenylene or phenylene group, which may contain a carbonyl, ester,ether or hydroxyl radical, M⁻ is a non-nucleophilic counter ion, d1, d2and d3 are in the range: 0≦d1≦0.5, 0≦d2≦0.5, 0≦d3≦0.5, and0<d1+d2+d3≦0.5.

More preferably, the polymer may further comprise recurring units of atleast one type selected from indene units (e1), acenaphthylene units(e2), chromone units (e3), coumarin units (e4), and norbornadiene units(e5), as represented by the general formula (9).

Herein R¹¹⁰ to R¹¹⁴ each are hydrogen, a C₁-C₃₀ alkyl, partially orentirely halo-substituted alkyl, hydroxyl, alkoxy, alkanoyl,alkoxycarbonyl, C₆-C₁₀ aryl, halogen, or1,1,1,3,3,3-hexafluoro-2-propanol group; X⁰ is methylene, oxygen orsulfur atom; e1 to e5 are numbers in the range: 0≦e1≦0.5, 0≦e2≦0.5,0≦e3≦0.5, 0≦e4≦0.5, O≦e5≦0.5, and 0<e1+e2+e3+e4+e5 0.5.

Typically, the resist composition may further comprise an organicsolvent, an acid generator, and optionally, a basic compound and/or asurfactant as an additive, the composition being a chemically amplifiedresist composition.

In a second aspect, the invention provides a monomer having the generalformula (4):

Herein R¹, R² and R³ are as defined above.

In a third aspect, the invention provides a polymer comprising recurringunits of the general formula (1) and having a weight average molecularweight of 1,000 to 500,000.

Herein R¹, R² and R³ are as defined above, and a is a number in therange: 0<a≦1.0.

Typically the polymer comprises recurring units (a) and acid labilegroup-substituted recurring units (b1) and/or (b2) copolymerizedtogether, as represented by the general formula (2), and has a weightaverage molecular weight of 1,000 to 500,000.

Herein R¹ to R⁹, Y¹, Y², p, q, a, b1 and b2 are as defined above.

In a fourth aspect, the invention provides a pattern forming processcomprising the steps of applying the positive resist composition definedabove onto a substrate to form a coating, baking, exposing the coatingto high-energy radiation, and developing the exposed coating in adeveloper.

Typically, the high-energy radiation is g- or i-line, KrF excimer laser,ArF excimer laser, electron beam or soft X-ray having a wavelength of 3to 15 nm.

The positive resist composition, typically chemically amplified positiveresist composition, may be used not only in the lithography for formingsemiconductor circuits, but also in the formation of mask circuitpatterns, micromachines, and thin-film magnetic head circuits.

ADVANTAGEOUS EFFECTS OF INVENTION

The positive resist composition has a satisfactory effect of suppressingacid diffusion and a high resolution, and forms a pattern of goodprofile and minimal edge roughness after exposure. The positive resistcomposition, typically chemically amplified positive resist compositionis best suited as a micropatterning material by lithography processesusing g-line, i-line, KrF excimer laser, EB or EUV for themicrofabrication of VLSI and photomasks.

DESCRIPTION OF EMBODIMENTS

As used herein, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. “Optional” or“optionally” means that the subsequently described event orcircumstances may or may not occur, and that description includesinstances where the event or circumstance occurs and instances where itdoes not. The notation (Cn-Cm) means a group containing from n to mcarbon atoms per group.

The acronym “PAG” stands for photoacid generator, “PEB” forpost-exposure bake, “LER” for line edge roughness, “LWR” for line widthroughness, “EUV” for extreme ultraviolet, and “EB” for electron beam.

One embodiment of the invention is a positive resist compositioncomprising a polymer comprising recurring units of the general formula(1) as a base resin.

Herein R¹ is a straight or branched C₁-C₄ alkylene group, R² ishydrogen, C₁-C₁₅ acyl group or acid labile group, R³ is hydrogen, methylor trifluoromethyl (CFO, and a is a number in the range: 0<a≦1.0.

Preferred as the base resin is a polymer comprising recurring units (a)and acid labile group-substituted recurring units (b1) and/or (b2)copolymerized together, as represented by the general formula (2). Thepolymer has a weight average molecular weight of 1,000 to 500,000.

Herein R¹, R² and R³ are as defined above, R⁴ and R⁶ each are hydrogenor methyl, R⁵ and R⁹ each are an acid labile group, R⁷ is a single bondor a straight or branched C₁-C₆ alkylene group, R⁸ is hydrogen,fluorine, trifluoromethyl, cyano, or straight, branched or cyclic C₁-C₆alkyl group, p is 1 or 2, q is an integer of 0 to 4, p+q≦5, Y¹ is asingle bond, a C₁-C₁₂ linking group having an ester radical, etherradical or lactone ring, phenylene group or naphthylene group, Y² is asingle bond, —C(═O)—O— or —C(═O)—NH—, a, b1 and b2 are numbers in therange: 0<a<1.0, 0≦b1<1.0, 0≦b2<1.0, 0<b1+b2<1.0, and 0.1≦a+b1+b2≦1.0.

A monomer Ma1 from which the recurring unit of formula (a) is derivedmay be represented by the following formula (4).

Herein R¹, R² and R³ are as defined above.

This monomer may be synthesized according to the following Scheme 1 or 2although the synthesis route is not limited thereto.

Herein R¹, R² and R³ are as defined above, R^(f1) is hydrogen or astraight, branched or cyclic, monovalent C₁-C₆ hydrocarbon group, X ishalogen, and M is Li, Na, K or substituted or unsubstituted ammonium.

The synthesis route of Scheme 1 is a substitution reaction betweenstyrene derivative (5) and carboxylic acid salt (6) to form the desiredmonomer Ma1. The reaction may be conducted in a standard way. Anappropriate amount of carboxylic acid salt (6) used is 0.5 to 10 moles,more preferably 1.0 to 3 moles per mole of styrene derivative (5). Ifthe amount of carboxylic acid salt (6) is less than 0.5 mole, a largefraction of the other reactant may be left unreacted, leading to asubstantial drop of percent yield. If the amount of carboxylic acid salt(6) exceeds 10 moles, the process may be uneconomical because ofincreased material costs and reduced pot yields.

The reaction of Scheme 1 may be conducted in a solvent. Suitablesolvents include hydrocarbons such as toluene, xylene, hexane andheptane; chlorinated solvents such as methylene chloride, chloroform,and dichloroethane; ethers such as diethyl ether, tetrahydrofuran anddibutyl ether; ketones such as acetone and 2-butanone; esters such asethyl acetate and butyl acetate; nitriles such as acetonitrile; alcoholssuch as methanol and ethanol; aprotic polar solvents such asN,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide; andwater, which may be used alone or in admixture of two or more. A phasetransfer catalyst such as tetrabutylammonium hydrogensulfate may beadded to the reaction system. An appropriate amount of the phasetransfer catalyst added is 0.0001 to 1.0 mole, more preferably 0.001 to0.5 mole per mole of styrene derivative (5). Less than 0.0001 mole ofthe catalyst may fail to achieve the catalytic effect whereas more than1.0 mole may be uneconomical because of increased material costs.

An appropriate reaction temperature may be selected for the substitutionreaction, depending on other reaction conditions, although it ispreferably from −70° C. to near the boiling point of the solvent, morepreferably from 0° C. to near the boiling point of the solvent. Sincenoticeable side reactions may occur at higher temperatures, it isimportant for gaining higher yields that the reaction run at atemperature which is low, but enough to ensure a practically acceptablereaction rate. It is desirable from the yield standpoint to continue thereaction to completion while monitoring the reaction by gaschromatography (GC) or thin layer chromatography (TLC), although thereaction time is usually about 30 minutes to about 40 hours. The monomerMa1 may be recovered from the reaction mixture by ordinary aqueouswork-up. If necessary, the monomer may be purified by standardtechniques like distillation, recrystallization and chromatography.

The synthesis route of Scheme 2 is an ester exchange reaction betweenstyrene derivative (7) and ester (8) to form the desired monomer Ma1.The reaction may be effected in a solventless system or in a solvent.Suitable solvents include ethers such as tetrahydrofuran, diethyl ether,di-n-butyl ether, and 1,4-dioxane, and hydrocarbons such as n-hexane,n-heptane, benzene, toluene, xylene and cumene, which may be used aloneor in admixture. Suitable catalysts include metal alkoxides such assodium methoxide, sodium ethoxide, potassium tert-butoxide, magnesiumethoxide, titanium(IV) methoxide, titanium(IV) ethoxide, andtitanium(IV) isopropoxide; organic amines such as triethylamine,N,N-dimethylaminopyridine and 1,8-diazabicyclo[5.4.0]-7-undecene; andinorganic bases such as sodium hydroxide, potassium carbonate and sodiumcarbonate, which may be used alone or in admixture. An appropriateamount of the catalyst added is 0.001 to 5.0 moles, more preferably0.001 to 0.1 mole per mole of ester (8). The reaction temperature varieswith other reaction conditions. Preferably reaction is conducted at atemperature of 50 to 200° C. while distilling off R^(f1) OH formedduring reaction. It is desirable from the yield standpoint to continuethe reaction to completion while monitoring the reaction by gaschromatography (GC) or silica gel thin layer chromatography (TLC),although the reaction time is usually about 30 minutes to about 20hours. The monomer Ma1 may be recovered from the reaction mixture byordinary aqueous work-up. If necessary, the monomer may be purified bystandard techniques like distillation, recrystallization andchromatography.

In formula (2), R² is hydrogen, a C₁-C₁₅ acyl group or an acid labilegroup. Suitable C₁-C₁₅ acyl groups include formyl, acetyl,ethylcarbonyl, pivaloyl, methoxycarbonyl, ethoxycarbonyl,tert-butoxycarbonyl, trifluoroacetyl and trichloroacetyl. The acidlabile group is described later.

Examples of the monomer Ma1 of formula (4) from which recurring unit (a)is derived are given below.

Herein R² is as defined above.

While the polymer is used in the positive resist composition, therecurring unit (a) is a unit of formula (1). Since this unit has aCF₃—C(OR²)—R³ group such as 1,1,1,3,3,3-hexafluoro-2-propanol which isbonded to an ester group, the acidity of hydroxyl moiety is high, ascompared with the CF₃—C(OR²)—R³ group such as1,1,1,3,3,3-hexafluoro-2-propanol which is not bonded to an ester group.The polymer is thus characterized by a high alkaline dissolution. Thepolymer is also characterized by a high sensitivity to EUV exposure, dueto good absorption of EUV light. Besides high sensitivity, the polymeris effective for suppressing pattern collapse due to swell duringdevelopment.

Monomers Mb1 and Mb2 from which the acid labile group-containingrecurring units (b1) and (b2) in formula (2) are derived may berepresented by the following formulae.

Herein R⁴ to R⁹, Y¹, Y², p and q are as defined above.

Of the groups represented by Y¹, the C₁-C₁₂ linking group having alactone ring may be exemplified by the following.

Examples of the monomer Mb1 from which recurring unit (b1) is derivedare given below, but not limited thereto.

Herein R⁴ and R⁵ are as defined above.

Examples of the monomer Mb2 from which recurring unit (b2) is derivedare given below, but not limited thereto.

Herein R⁶ and R⁹ are as defined above.

The acid labile groups represented by R², R⁵ and R⁹ in formula (2) maybe selected from a variety of such groups. The acid labile groups may bethe same or different and preferably include substituent groups of thefollowing formulae (A-1) to (A-3).

In formula (A-1), R^(L30) is a tertiary alkyl group of 4 to 20 carbonatoms, preferably 4 to 15 carbon atoms, a trialkylsilyl group in whicheach alkyl moiety has 1 to 6 carbon atoms, an oxoalkyl group of 4 to 20carbon atoms, or a group of formula (A-3). Exemplary tertiary alkylgroups are tert-butyl, tert-amyl, 1,1-diethylpropyl, 1-ethylcyclopentyl,1-butylcyclopentyl, 1-ethylcyclohexyl, 1-butylcyclohexyl,1-ethyl-2-cyclopentenyl, 1-ethyl-2-cyclohexenyl, and2-methyl-2-adamantyl. Exemplary trialkylsilyl groups are trimethylsilyl,triethylsilyl, and dimethyl-tert-butylsilyl. Exemplary oxoalkyl groupsare 3-oxocyclohexyl, 4-methyl-2-oxooxan-4-yl, and5-methyl-2-oxooxolan-5-yl. Letter A1 is an integer of 0 to 6.

In formula (A-2), R^(L31) and R^(L32) are hydrogen or straight, branchedor cyclic alkyl groups of 1 to 18 carbon atoms, preferably 1 to 10carbon atoms. Exemplary alkyl groups include methyl, ethyl, propyl,isopropyl, n-butyl, sec-butyl, tert-butyl, cyclopentyl, cyclohexyl,2-ethylhexyl, and n-octyl. R^(L33) is a monovalent hydrocarbon group of1 to 18 carbon atoms, preferably 1 to 10 carbon atoms, which may containa heteroatom such as oxygen, examples of which include straight,branched or cyclic alkyl groups and substituted forms of such alkylgroups in which some hydrogen atoms are replaced by hydroxyl, alkoxy,oxo, amino, alkylamino or the like. Illustrative examples of thesubstituted alkyl groups are shown below.

A pair of R^(L31) and R^(L32), R^(L31) and R^(L33), or R^(L32) andR^(L33) may bond together to form a ring with the carbon and oxygenatoms to which they are attached. Each of R^(L31), R^(L32) and R^(L33)is a straight or branched alkylene group of 1 to 18 carbon atoms,preferably 1 to 10 carbon atoms when they form a ring, while the ringpreferably has 3 to 10 carbon atoms, more preferably 4 to 10 carbonatoms.

Examples of the acid labile groups of formula (A-1) includetert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl,tert-amyloxycarbonylmethyl, 1,1-diethylpropyloxycarbonyl,1,1-diethylpropyloxycarbonylmethyl, 1-ethylcyclopentyloxycarbonyl,1-ethylcyclopentyloxycarbonylmethyl, 1-ethyl-2-cyclopentenyloxycarbonyl,1-ethyl-2-cyclopentenyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl,2-tetrahydropyranyloxycarbonylmethyl, and2-tetrahydrofuranyloxycarbonylmethyl.

Also included are substituent groups having the formulae (A-1)-1 to(A-1)-10.

Herein R^(L37) is each independently a straight, branched or cyclicC₁-C₁₀ alkyl group or C₆-C₂₀ aryl group, R^(L38) is hydrogen or astraight, branched or cyclic C₁-C₁₀ alkyl group, R^(L39) is eachindependently a straight, branched or cyclic C₂-C₁₀ alkyl group orC₆-C₂₀ aryl group, and A1 is as defined above.

Of the acid labile groups of formula (A-2), the straight and branchedones are exemplified by the following groups having formulae (A-2)-1 to(A-2)-69.

Of the acid labile groups of formula (A-2), the cyclic ones are, forexample, tetrahydrofuran-2-yl, 2-methyltetrahydrofuran-2-yl,tetrahydropyran-2-yl, and 2-methyltetrahydropyran-2-yl.

Other examples of acid labile groups include those of the generalformula (A-2a) or (A-2b) while the polymer may be crosslinked within themolecule or between molecules with these acid labile groups.

Herein R^(L40) and R^(L41) each are hydrogen or a straight, branched orcyclic C₁-C₈ alkyl group, or R^(L40) and R^(L41), taken together, mayform a ring with the carbon atom to which they are attached, and R^(L40)and R^(L41) are straight or branched C₁-C₈ alkylene groups when theyform a ring. R^(L42) is a straight, branched or cyclic C₁-C₁₀ alkylenegroup. Each of B1 and D1 is 0 or an integer of 1 to 10, preferably 0 oran integer of 1 to 5, and C1 is an integer of 1 to 7. “A” is a(C1+1)-valent aliphatic or alicyclic saturated hydrocarbon group,aromatic hydrocarbon group or heterocyclic group having 1 to 50 carbonatoms, which may be separated by a heteroatom or in which some of thehydrogen atoms attached to carbon atoms may be substituted by hydroxyl,carboxyl, carbonyl groups or fluorine atoms. “B” is —CO—O—, —NHCO—O— or—NHCONH—.

Preferably, “A” is selected from divalent to tetravalent, straight,branched or cyclic C₁-C₂₀ alkylene, alkyltriyl and alkyltetrayl groups,and C₆-C₃₀ arylene groups, which may be separated by a heteroatom or inwhich some of the hydrogen atoms attached to carbon atoms may besubstituted by hydroxyl, carboxyl, acyl groups or halogen atoms. Thesubscript C1 is preferably an integer of 1 to 3.

The crosslinking acetal groups of formulae (A-2a) and (A-2b) areexemplified by the following formulae (A-2)-70 through (A-2)-77.

In formula (A-3), R^(L34), R^(L35) and R^(L36) each are a monovalenthydrocarbon group, typically a straight, branched or cyclic C₁-C₂₀ alkylgroup or straight, branched or cyclic C₂-C₂₀ alkenyl group, which maycontain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. Apair of R^(L34) and R^(L35), R^(L34) and R^(L36), or R^(L35) and R^(L36)may bond together to form a C₃-C₂₀ aliphatic ring with the carbon atomto which they are attached.

Exemplary tertiary alkyl groups of formula (A-3) include tert-butyl,triethylcarbyl, 1-ethylnorbornyl, 1-methylcyclohexyl,1-ethylcyclopentyl, 2-(2-methyl)adamantyl, 2-(2-ethyl)adamantyl, andtert-amyl.

Other exemplary tertiary alkyl groups include those of the followingformulae (A-3)-1 to (A-3)-18.

Herein R^(L43) is each independently a straight, branched or cyclicC₁-C₈ alkyl group or C₆-C₂₀ aryl group, typically phenyl, R^(L44) andR^(L46) each are hydrogen or a straight, branched or cyclic C₁-C₂₀ alkylgroup, and R^(L45) is a C₆-C₂₀ aryl group, typically phenyl.

The polymer may be crosslinked within the molecule or between moleculeswith groups having R^(L47) which is a di- or multi-valent alkylene orarylene group, as shown by the following formulae (A-3)-19 and (A-3)-20.

Herein R^(L43) is as defined above, R^(L47) is a straight, branched orcyclic C₁-C₂₀ alkylene group or arylene group, typically phenylene,which may contain a heteroatom such as oxygen, sulfur or nitrogen, andE1 is an integer of 1 to 3.

Of recurring units having acid labile groups of formula (A-3), recurringunits of (meth)acrylate having an exo-form structure represented by theformula (A-3)-21 are preferred.

Herein, R⁴ is hydrogen or methyl; R^(Lc3) is a straight, branched orcyclic C₁-C₈ alkyl group or an optionally substituted C₆-C₂₀ aryl group;R^(Lc4) to R^(Lc9), R^(Lc12) and R^(Lc13) are each independentlyhydrogen or a monovalent C₁-C₁₅ hydrocarbon group which may contain aheteroatom; and R^(L10) and R^(Lc11) are hydrogen or a monovalent C₁-C₁₅hydrocarbon group which may contain a heteroatom. Alternatively, a pairof R^(Lc4) and R^(Lc5), R^(Lc6) and R^(Lc8), R^(Lc6) and R^(Lc9),R^(Lc7) and R^(Lc9), R^(Lc7) and R^(Lc13), R^(Lc8) and R^(Lc12),R^(Lc10) and R^(Lc11), or R^(Lc11) and R^(Lc12) taken together, may forma ring, and in that event, each ring-forming R is a divalent C₁-C₁₅hydrocarbon group which may contain a heteroatom. Also, a pair ofR^(Lc4) and R^(Lc13), R^(Lc10) and R^(Lc13), or R^(Lc6) and R^(Lc8)which are attached to vicinal carbon atoms may bond together directly toform a double bond. The formula also represents an enantiomer.

The ester form monomers from which recurring units having an exo-formstructure represented by formula (A-3)-21 are derived are described inU.S. Pat. No. 6,448,420 (JP-A 2000-327633). Illustrative non-limitingexamples of suitable monomers are given below.

Also included in the acid labile groups of formula (A-3) are acid labilegroups of (meth)acrylate having furandiyl, tetrahydrofurandiyl oroxanorbornanediyl as represented by the following formula (A-3)-22.

Herein, R⁴ is as defined above; R^(Lc14) and R^(Lc15) are eachindependently a monovalent, straight, branched or cyclic C₁-C₁₀hydrocarbon group, or R^(Lc14) and R^(Lc15), taken together, may form analiphatic hydrocarbon ring with the carbon atom to which they areattached. R^(Lc16) is a divalent group selected from furandiyl,tetrahydrofurandiyl and oxanorbornanediyl. R^(Lc17) is hydrogen or amonovalent, straight, branched or cyclic C₁-C₁₀ hydrocarbon group whichmay contain a heteroatom.

Examples of the monomers from which the recurring units substituted withacid labile groups having furandiyl, tetrahydrofurandiyl andoxanorbornanediyl are derived are shown below. Note that Me is methyland Ac is acetyl.

In the recurring unit (b1), the hydrogen atom of the carboxyl group maybe substituted by an acid labile group having the general formula(A-3)-23.

Herein R²³⁻¹ is hydrogen, C₁-C₄, alkyl, alkoxy, alkanoyl,alkoxycarbonyl, C₆-C₁₀ aryl, halogen, or cyano group, and m23 is aninteger of 1 to 4.

Examples of the monomer having a carboxyl group substituted with an acidlabile group of formula (A-3)-23 are given below.

In the recurring unit (b1), the hydrogen atom of the carboxyl group maybe substituted by an acid labile group having the general formula(A-3)-24.

Herein R²⁴⁻¹ and R²⁴⁻² each are hydrogen, C₁-C₄ alkyl, alkoxy, alkanoyl,alkoxycarbonyl, hydroxyl, C₆-C₁₀ aryl, halogen, or cyano group; R ishydrogen, a straight, branched or cyclic C₁-C₁₂ alkyl group which maycontain an oxygen or sulfur atom, C₂-C₁₂ alkenyl, C₂-C₁₂ alkynyl, orC₆-C₁₀ aryl group; R²⁴⁻³, R²⁴⁻⁴, R²⁴⁻⁵, and R²⁴⁻⁶ each are hydrogen, ora pair of R²⁴⁻³ and R²⁴⁻⁴, R²⁴⁻⁴ and R²⁴⁻⁵, or R²⁴⁻⁵ and R²⁴⁻⁶ may bondtogether to form a benzene ring; m24 and n24 each are an integer of 1 to4.

Examples of the monomer having a carboxyl group substituted with an acidlabile group of formula (A-3)-24 are given below.

In the recurring unit (b1), the hydrogen atom of the carboxyl group maybe substituted by an acid labile group having the general formula(A-3)-25.

Herein R²⁵⁻¹ is each independently hydrogen or a straight, branched orcyclic C₁-C₆ alkyl group, and in case m25 is 2 or more, R²⁵⁻¹ may bondtogether to form a non-aromatic ring of 2 to 8 carbon atoms; the circledenotes a link between carbons C_(A) and C_(B), selected from amongethylene, propylene, butylene and pentylene; R²⁵⁻¹ is not hydrogen whenthe circle denotes ethylene or propylene; R²⁵⁻² is C₁-C₄, alkyl, alkoxy,alkanoyl, alkoxycarbonyl, hydroxyl, nitro, C₆-C₁₀ aryl, halogen, orcyano group; R is as defined above; m25 and n25 each are an integer of 1to 4.

Examples of the monomer having a carboxyl group substituted with an acidlabile group of formula (A-3)-25 are given below.

In the recurring unit (b1), the hydrogen atom of the carboxyl group maybe substituted by an acid labile group having the general formula(A-3)-26.

Herein R²⁶⁻¹ and R²⁶⁻² each are hydrogen, C₁-C₄ alkyl, alkoxy, alkanoyl,alkoxycarbonyl, hydroxyl, nitro, C₆-C₁₀ aryl, halogen, or cyano group; Ris as defined above; and m26 and n26 each are an integer of 1 to 4.

Examples of the monomer having a carboxyl group substituted with an acidlabile group of formula (A-3)-26 are given below.

In the recurring unit (b1), the hydrogen atom of the carboxyl group maybe substituted by an acid labile group having the general formula(A-3)-27.

Herein R²⁷⁻¹ and R²⁷⁻² each are hydrogen, C₁-C₄ alkyl, alkoxy, alkanoyl,alkoxycarbonyl, hydroxyl, C₆-C₁₀ aryl, halogen, or cyano group; R is asdefined above; J is methylene, ethylene, vinylene or —CH₂—S—; and m27and n27 each are an integer of 1 to 4.

Examples of the monomer having a carboxyl group substituted with an acidlabile group of formula (A-3)-27 are given below.

In the recurring unit (b1), the hydrogen atom of the carboxyl group maybe substituted by an acid labile group having the general formula(A-3)-28.

Herein R²⁸⁻¹ and R²⁸⁻² each are hydrogen, C₁-C₄ alkyl, alkoxy, alkanoyl,alkoxycarbonyl, hydroxyl, C₆-C₁₀ aryl, halogen, or cyano group; R is asdefined above; K is carbonyl, ether, sulfide, —S(═O)— or —S(═O)₂—; andm28 and n28 each are an integer of 1 to 4.

Examples of the monomer having a carboxyl group substituted with an acidlabile group of formula (A-3)-28 are given below.

Also included are fluorinated acid labile groups as shown below.

In a more preferred embodiment, the polymer as the base resin mayfurther comprise recurring units (c) having an adhesive group ascopolymerized with the recurring units (a) and the recurring units (b1)having a carboxyl group substituted with an acid labile group and/or therecurring units (b2) having a phenolic hydroxyl group substituted withan acid labile group, as represented by formula (2). The adhesive groupis selected from among hydroxyl, carboxyl, lactone ring, carbonate,thiocarbonate, carbonyl, cyclic acetal, ether, ester, sulfonic acidester, cyano, amide, and —O—C(═O)-G- wherein G is sulfur or NH; and c isa number in the range: 0<c≦0.9 and 0.2≦a+b1+b2+c≦1.0. The polymer has aweight average molecular weight in the range of 1,000 to 500,000.

Shown below are examples of the monomer from which the recurring units(c) having an adhesive group selected from among hydroxyl, carboxyl,lactone ring, carbonate, thiocarbonate, carbonyl, cyclic acetal, ether,ester, sulfonic acid ester, cyano, amide, and —O—C(═O)-G- wherein G issulfur or NH are derived.

In the case of a monomer having a hydroxyl group, the hydroxyl group maybe replaced by an acetal group susceptible to deprotection with acid,typically ethoxyethoxy, prior to polymerization, and the polymerizationbe followed by deprotection with weak acid and water. Alternatively, thehydroxyl group may be replaced by an acetyl, formyl, pivaloyl or similargroup prior to polymerization, and the polymerization be followed byalkaline hydrolysis.

In a more preferred embodiment, recurring units (d1), (d2) or (d3)having a sulfonium salt as represented by the following general formula(3) may be copolymerized. It is noted that JP-A 2006-045311 discloses asulfonium or iodonium salt having polymerizable olefin capable ofgenerating a specific sulfonic acid; and JP-A 2006-178317 discloses asulfonium salt having sulfonic acid directly attached to the main chain.

Herein R²⁰, R²⁴, and R^(H) each are hydrogen or methyl. R²¹ is a singlebond, phenylene, —O—R—, or —C(═O)—Y⁰—R—. Y⁰ is oxygen or NH. R is astraight, branched or cyclic C₁-C₆ alkylene group, alkenylene group orphenylene group, which may contain a carbonyl (—CO—), ester (—COO—),ether (—O—), or hydroxyl moiety. R²², R²³, R²⁵, R²⁶, R²⁷, R²⁹, R³⁰, andR³¹ are each independently a straight, branched or cyclic C₁-C₁₂ alkylgroup which may contain a carbonyl, ester or ether moiety, a C₆-C₁₂ arylgroup, a C₇-C₂₀ aralkyl group, or a thiophenyl group. Z⁰ is a singlebond, methylene, ethylene, phenylene, fluorinated phenylene, —O—R³²—, or—C(═O)—Z¹—R³²—, wherein Z¹ is oxygen or NH, and R³² is a straight,branched or cyclic C₁-C₆ alkylene group, alkenylene group or phenylenegroup, which may contain a carbonyl, ester, ether or hydroxyl moiety. Mis a non-nucleophilic counter ion. Molar fractions d1, d2 and d3 are inthe range: 0≦d1≦0.5, 0≦d2≦0.5, 0≦d3≦0.5, 0≦d1+d2+d3≦0.5. When recurringunits (d1), (d2) or (d3) are incorporated, the preferred range is0<d1+d2+d3≦0.5 and 0.2≦a+b1+b2+c+d1+d2+d3≦1.0.

Binding an acid generator to the polymer backbone is effective forreducing acid diffusion and preventing the resolution from lowering dueto blur by acid diffusion. Additionally, edge roughness (LER, LWR) isimproved because the acid generator is uniformly dispersed.

Examples of the non-nucleophilic counter ion represented by M⁻ includehalide ions such as chloride and bromide ions; fluoroalkylsulfonate ionssuch as triflate, 1,1,1-trifluoroethanesulfonate, andnonafluorobutanesulfonate; arylsulfonate ions such as tosylate,benzenesulfonate, 4-fluorobenzenesulfonate, and1,2,3,4,5-pentafluorobenzenesulfonate; alkylsulfonate ions such asmesylate and butanesulfonate; imidates such asbis(trifluoromethylsulfonyl)imide, bis(perfluoroethylsulfonyl)imide andbis(perfluorobutylsulfonyl)imide; methidates such astris(trifluoromethylsulfonyl)methide andtris(perfluoroethylsulfonyl)methide.

Other non-nucleophilic counter ions include sulfonates having fluorinesubstituted at α-position as represented by the general formula (K-1)and sulfonates having fluorine substituted at α- and β-positions asrepresented by the general formula (K-2).

In formula (K-1), R¹⁰² is hydrogen, or a straight, branched or cyclicC₁-C₂₀ alkyl group, C₂-C₂₀ alkenyl group, or C₆-C₂₀ aryl group, whichmay have an ether, ester, carbonyl moiety, lactone ring or fluorine. Informula (K-2), R¹⁰³ is hydrogen, or a straight, branched or cyclicC₁-C₃₀ alkyl or acyl group, C₂-C₂₀ alkenyl group, or C₆-C₂₀ aryl oraryloxy group, which may have an ether, ester, carbonyl moiety orlactone ring.

Understandably, when a polymer having copolymerized therein recurringunits of any type as represented by formula (3) is used as the baseresin in a resist composition, the addition of a photoacid generator tobe described later may be omitted.

The polymer may have further copolymerized therein recurring units (e)of any type selected from indene units (e1), acenaphthylene units (e2),chromone units (e3), coumarin units (e4), and norbornadiene units (e5)as represented by the general formula (9).

Herein R¹¹⁰ to R¹¹⁴ each are hydrogen, C₁-C₃₀ alkyl, partially orentirely halo-substituted alkyl, hydroxyl, alkoxy, alkanoyl,alkoxycarbonyl, C₆-C₁₀ aryl, halogen, or1,1,1,3,3,3-hexafluoro-2-propanol group; X° is methylene, oxygen orsulfur atom; e1 to e5 are numbers in the range: 0≦e1≦0.5, 0≦e2≦0.5,0≦e3≦0.5, 0≦e4≦0.5, 0≦e5≦0.5, and 0<e1+e2+e3+e4+e5≦0.5.

Besides the recurring units (a) to (e), additional recurring units (f)may be copolymerized in the polymer. Exemplary are recurring unitsderived from styrene, vinylnaphthalene, vinylanthracene, vinylpyrene,methyleneindane, and the like.

The polymer defined herein may be synthesized by any desired methods,for example, by dissolving suitable monomers selected from the monomersto form the recurring units (a) to (f) in an organic solvent, adding aradical polymerization initiator thereto, and effecting heatpolymerization. Examples of the organic solvent which can be used forpolymerization include toluene, benzene, tetrahydrofuran, diethyl ether,dioxane, cyclohexane, cyclopentane, methyl ethyl ketone, andγ-butyrolactone. Examples of the polymerization initiator used hereininclude 2,2′-azobisisobutyronitrile (AIBN),2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide.Preferably the system is heated at 50 to 80° C. for polymerization totake place. The reaction time is 2 to 100 hours, preferably 5 to 20hours.

When hydroxystyrene or hydroxyvinylnaphthalene is copolymerized, analternative method is possible. Specifically, acetoxystyrene oracetoxyvinylnaphthalene is used instead of hydroxystyrene orhydroxyvinylnaphthalene, and after polymerization, the acetoxy group isdeprotected by alkaline hydrolysis as mentioned above, for therebyconverting the polymer product to polyhydroxystyrene orhydroxypolyvinylnaphthalene. For alkaline hydrolysis, a base such asaqueous ammonia or triethylamine may be used. The reaction temperatureis −20° C. to 100° C., preferably 0° C. to 60° C., and the reaction timeis 0.2 to 100 hours, preferably 0.5 to 20 hours.

In the (co)polymer, recurring units (a) to (c) may be incorporated inthe following molar fraction: 0<a≦1.0, preferably 0<a<1.0, 0≦b1<1.0,0≦b2<1.0, 0<b1+b2<1.0, 0.1≦a+b1+b2≦1.0, and 0≦c≦0.9;

where unit (c) is incorporated, 0<c≦0.9 and 0.2≦a+b1+b2+c1.0;more preferably 0.02≦a≦0.8, 0≦b1≦0.8, 0≦b2≦0.8, 0.1≦b1+b2≦0.8,0.1≦c≦0.88;even more preferably 0.05≦a≦0.75, 0≦b1≦0.7, 0≦b2≦0.7, 0.1≦b1+b2≦0.75,0.15≦c≦0.85; andmost preferably 0.07≦a≦0.7, 0≦b1≦0.65, 0≦b2≦0.65, 0.1≦b1+b2≦0.7,0.2≦c≦0.83.

Where unit (d) is incorporated, the range is 0≦d1≦0.5, 0≦d2≦0.5,0≦d3≦0.5, and 0≦d1+d2+d3≦0.5; preferably 0≦d1≦0.4, 0≦d20.4, 0≦d3≦0.4,and 0≦d1+d2+d3≦0.4; more preferably 0≦d1≦0.3, 0≦d2≦0.3, 0≦d3≦0.3, and0≦d1+d2+d3≦0.3; and even more preferably 0≦d1≦0.2, 0≦d2≦0.2, 0≦d3≦0.2,and 0≦d1+d2+d3≦0.25.

Where recurring units (e) and (f) are incorporated, their molar fractionis: 0≦e1≦0.5, 0≦e2≦0.5, 0≦e3≦0.5, 0≦e4 0.5, 0≦e5≦0.5, and0≦e1+e2+e3+e4+e5≦0.5; preferably 0≦e1≦0.4, 0≦e2≦0.4, 0≦e3≦0.4, 0≦e4≦0.4,0≦e5≦0.4, and 0≦e1+e2+e3+e4+e5≦0.4; more preferably 0≦e1≦0.3, 0≦e2≦0.3,0≦e3≦0.3, 0≦e4≦0.3, 0≦e5≦0.3, and 0≦e1+e2+e3+e4+e5≦0.3; and 0≦f≦0.5,preferably 0≦f≦0.4, more preferably 0≦f≦0.3. It is preferred thata+b1+b2+c+d1+d2+d3+e1+e2+e3+e4+e5+f=1.

The polymer serving as the base resin in the positive resist compositionshould have a weight average molecular weight (Mw) in the range of 1,000to 500,000, and preferably 2,000 to 30,000, as measured by gelpermeation chromatography (GPC) versus polystyrene standards usingtetrahydrofuran as a solvent. With too low a Mw, the resist compositionbecomes less heat resistant. A polymer with too high a Mw loses alkalinesolubility and gives rise to a footing phenomenon after patternformation.

If a multi-component polymer has a wide molecular weight distribution ordispersity (Mw/Mn), which indicates the presence of lower and highermolecular weight polymer fractions, there is a possibility that foreignmatter is left on the pattern or the pattern profile is degraded. Theinfluences of molecular weight and dispersity become stronger as thepattern rule becomes finer. Therefore, the multi-component copolymershould preferably have a narrow dispersity (Mw/Mn) of 1.0 to 2.0,especially 1.0 to 1.5, in order to provide a resist composition suitablefor micropatterning to a small feature size.

It is understood that a blend of two or more polymers which differ incompositional ratio, molecular weight or dispersity is acceptable aswell as a blend of an inventive polymer and a polymer free of recurringunits (a).

The polymer is advantageously used as a base resin in a positive resistcomposition, typically chemically amplified positive resist composition.Specifically, the polymer is used as a base resin and combined with anydesired components including an organic solvent, acid generator,dissolution regulator, basic compound, surfactant, and acetylene alcoholto formulate a resist composition. This positive resist composition hasa very high sensitivity in that the dissolution rate in developer of thepolymer in exposed areas is accelerated by catalytic reaction. Inaddition, the resist film has a high dissolution contrast, resolution,exposure latitude, and process adaptability, and provides a good patternprofile after exposure, yet better etching resistance, and minimalproximity bias because of restrained acid diffusion. By virtue of theseadvantages, the composition is fully useful in commercial applicationand suited as a pattern-forming material for the fabrication of VLSIs orphotomasks.

Particularly when an acid generator is added to formulate a chemicallyamplified positive resist composition capable of utilizing acidcatalyzed reaction, the composition has a higher sensitivity and isfurther improved in the properties described above. Typical of the acidgenerator used herein is a photoacid generator (PAG) capable ofgenerating an acid in response to actinic light or radiation. It is anycompound capable of generating an acid upon exposure to high-energyradiation. Suitable photoacid generators include sulfonium salts,iodonium salts, sulfonyldiazomethane, N-sulfonyloxyimide, andoxime-O-sulfonate acid generators. The acid generators may be used aloneor in admixture of two or more. Exemplary acid generators are describedin U.S. Pat. No. 7,537,880 (JP-A 2008-111103, paragraphs [0122] to[0142]).

Inclusion of a dissolution regulator may lead to an increased differencein dissolution rate between exposed and unexposed areas and a furtherimprovement in resolution. Addition of a basic compound may be effectivein suppressing the diffusion rate of acid in the resist film, achievinga further improvement in resolution. Addition of a surfactant mayimprove or control the coating characteristics of the resistcomposition.

Examples of the organic solvent used herein are described in JP-A2008-111103, paragraphs [0144] to [0145] (U.S. Pat. No. 7,537,880).Exemplary basic compounds are described in JP-A 2008-111103, paragraphs[0146] to [0164]. Exemplary surfactants are described in JP-A2008-111103, paragraphs to [0166]. Exemplary dissolution regulators aredescribed in JP-A 2008-122932 (US 2008090172), paragraphs to [0178], andexemplary acetylene alcohols in paragraphs [0179] to [0182]. Also usefulare quenchers of polymer type as described in JP-A 2008-239918. Thepolymeric quencher segregates at the resist surface after coating andthus enhances the rectangularity of resist pattern. When a protectivefilm is applied, the polymeric quencher is also effective for preventinga film thickness loss of resist pattern or rounding of pattern top.

An appropriate amount of the acid generator used is 0.01 to 100 parts,and preferably 0.1 to 80 parts. An appropriate amount of the organicsolvent used is 50 to 10,000 parts, especially 100 to 5,000 parts. Thedissolution regulator may be blended in an amount of 0 to 50 parts,preferably 0 to 40 parts, the basic compound in an amount of 0 to 100parts, preferably 0.001 to 50 parts, and the surfactant in an amount of0 to 10 parts, preferably 0.0001 to 5 parts. All amounts are expressedin parts by weight relative to 100 parts by weight of the base resin.

Process

The positive resist composition, typically chemically amplified positiveresist composition is used in the fabrication of various integratedcircuits. Pattern formation using the resist composition may beperformed by well-known lithography processes. The process generallyinvolves coating, heat treatment (or prebaking), exposure, heattreatment (PEB), and development. If necessary, any additional steps maybe added.

The resist composition is first applied onto a substrate on which anintegrated circuit is to be formed (e.g., Si, SiO₂, SiN, SiON, TiN, WSi,BPSG, SOG, or organic antireflective coating) or a substrate on which amask circuit is to be formed (e.g., Cr, CrO, CrON, or MoSi) by asuitable coating technique such as spin coating, roll coating, flowcoating, dip coating, spray coating or doctor coating. The coating isprebaked on a hot plate at a temperature of 60 to 150° C. for 10 secondsto 30 minutes, preferably 80 to 120° C. for 30 seconds to 20 minutes.The resulting resist film is generally 0.1 to 2.0 μm thick.

If desired, a protective film may be formed on the resist film. Theprotective film is preferably formed of an alkaline developer-solublecomposition so that both formation of a resist pattern and stripping ofthe protective film may be achieved during development. The protectivefilm has the functions of restraining outgassing from the resist film,filtering or cutting off out-of-band (OOB) light having a wavelength of140 to 300 nm emitted by the EUV laser (other than 13.5 nm), andpreventing the resist film from assuming T-top profile or from losingits thickness under environmental impacts.

The resist film is then exposed to a desired pattern of high-energyradiation such as UV, deep-UV, EB, x-ray, excimer laser light, γ-ray,synchrotron radiation or EUV (soft x-ray), directly or through a mask.The exposure dose is preferably about 1 to 200 mJ/cm², more preferablyabout 10 to 100 mJ/cm², or 0.1 to 100 μC/cm², more preferably 0.5 to 50μC/cm². The resist film is further baked (PEB) on a hot plate at 60 to150° C. for 10 seconds to 30 minutes, preferably 80 to 120° C. for 30seconds to 20 minutes.

Thereafter the resist film is developed with a developer in the form ofan aqueous base solution for 3 seconds to 3 minutes, preferably 5seconds to 2 minutes by conventional techniques such as dip, puddle orspray techniques. Suitable developers are 0.1 to 10 wt %, preferably 2to 5 wt % aqueous solutions of tetramethylammonium hydroxide (TMAH),tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide(TPAH) and tetrabutylammonium hydroxide (TBAH). The resist film in theexposed area is dissolved in the developer whereas the resist film inthe unexposed area is not dissolved. In this way, the desired positivepattern is formed on the substrate. It is appreciated that the resistcomposition of the invention is best suited for micro-patterning usingsuch high-energy radiation as EB, EUV (soft x-ray), x-ray, γ-ray andsynchrotron radiation among others.

Although TMAH aqueous solution is generally used as the developer, TEAH,TPAH and TBAH having a longer alkyl chain are effective in inhibitingthe resist film from being swollen during development and thuspreventing pattern collapse. JP 3429592 describes an example using anaqueous TBAH solution for the development of a polymer comprisingrecurring units having an alicyclic structure such as adamantanemethacrylate and recurring units having an acid labile group such astert-butyl methacrylate, the polymer being water repellent due to theabsence of hydrophilic groups.

The TMAH developer is most often used as 2.38 wt % aqueous solution,which corresponds to 0.26 N. The TEAH, TPAH, and TBAH aqueous solutionsshould preferably have an equivalent normality. The concentration ofTEAR, TPAH, and TBAH that corresponds to 0.26N is 3.84 wt %, 5.31 wt %,and 6.78 wt %, respectively.

When a pattern with a line size of 32 nm or less is resolved by the EBand EUV lithography, there arises a phenomenon that lines become wavy,lines merge together, and merged lines collapse. It is believed thatthis phenomenon occurs because lines are swollen in the developer andthe thus expanded lines merge together. Since the swollen linescontaining liquid developer are as soft as sponge, they readily collapseunder the stress of rinsing. For this reason, the developer using along-chain alkyl developing agent is effective for preventing film swelland hence, pattern collapse.

In another embodiment, a negative pattern can be formed from the resistcomposition by organic solvent development. The developer used to thisend is at least one solvent selected from the group consisting of2-octanone, 2-nonanone, 2-heptanone, 3-heptanone, 4-heptanone,2-hexanone, 3-hexanone, diisobutyl ketone, methylcyclohexanone,acetophenone, methylacetophenone, propyl acetate, butyl acetate,isobutyl acetate, amyl acetate, butenyl acetate, isoamyl acetate, phenylacetate, propyl formate, butyl formate, isobutyl formate, amyl formate,isoamyl formate, methyl valerate, methyl pentenoate, methyl crotonate,ethyl crotonate, methyl propionate, ethyl propionate, ethyl3-ethoxypropionate, methyl lactate, ethyl lactate, propyl lactate, butyllactate, isobutyl lactate, amyl lactate, isoamyl lactate, methyl2-hydroxyisobutyrate, ethyl 2-hydroxyisobutyrate, methyl benzoate, ethylbenzoate, benzyl acetate, methyl phenylacetate, benzyl formate,phenylethyl formate, methyl 3-phenylpropionate, benzyl propionate, ethylphenylacetate, and 2-phenylethyl acetate.

At the end of development, the resist film is rinsed. As the rinsingliquid, a solvent which is miscible with the developer and does notdissolve the resist film is preferred. Suitable solvents includealcohols of 3 to 10 carbon atoms, ether compounds of 8 to 12 carbonatoms, alkanes, alkenes, and alkynes of 6 to 12 carbon atoms, andaromatic solvents. Specifically, suitable alkanes of 6 to 12 carbonatoms include hexane, heptane, octane, nonane, decane, undecane,dodecane, methylcyclopentane, dimethylcyclopentane, cyclohexane,methylcyclohexane, dimethylcyclohexane, cycloheptane, cyclooctane, andcyclononane. Suitable alkenes of 6 to 12 carbon atoms include hexene,heptene, octene, cyclohexene, methylcyclohexene, dimethylcyclohexene,cycloheptene, and cyclooctene. Suitable alkynes of 6 to 12 carbon atomsinclude hexyne, heptyne, and octyne. Suitable alcohols of 3 to 10 carbonatoms include n-propyl alcohol, isopropyl alcohol, 1-butyl alcohol,2-butyl alcohol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol,2-pentanol, 3-pentanol, tert-amyl alcohol, neopentyl alcohol,2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-3-pentanol,cyclopentanol, 1-hexanol, 2-hexanol, 3-hexanol, 2,3-dimethyl-2-butanol,3,3-dimethyl-1-butanol, 3,3-dimethyl-2-butanol, 2-ethyl-1-butanol,2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol,3-methyl-1-pentanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol,4-methyl-1-pentanol, 4-methyl-2-pentanol, 4-methyl-3-pentanol,cyclohexanol, and 1-octanol. Suitable ether compounds of 8 to 12 carbonatoms include di-n-butyl ether, diisobutyl ether, di-sec-butyl ether,di-n-pentyl ether, diisopentyl ether, di-sec-pentyl ether, di-t-amylether, and di-n-hexyl ether. Suitable aromatic solvents include toluene,xylene, ethylbenzene, isopropylbenzene, t-butylbenzene, and mesitylene.The solvents may be used alone or in admixture.

EXAMPLE

Synthesis Examples, Comparative Synthesis Examples, Examples andComparative Examples are given below for further illustrating theinvention, but they should not be construed as limiting the inventionthereto. Mw is a weight average molecular weight as measured by gelpermeation chromatography (GPC) versus polystyrene standards, and Mw/Mndesignates molecular weight distribution or dispersity. All parts (pbw)are by weight.

Monomer Synthesis Example 1 Synthesis of Monomer 1

In 300 g of acetonitrile were dissolved 56.7 g ofp-(chloromethyl)styrene, 100 g of sodium3,3,3-trifluoro-2-hydroxy-2-trifluoromethylpropionate, and 2.8 g ofsodium iodide. The contents were stirred for one day at an internaltemperature of 40-50° C. To the reaction solution, 200 g of 5 wt %hydrochloric acid was added to quench the reaction, followed by standardaqueous workup. The solvent was distilled off. The product was purifiedby distillation, obtaining 103.6 g (yield 85%) of Monomer 1.

boiling point: 52-53° C./12 Pa

IR (D-ATR): v=3465, 3093, 3012, 1757, 1515, 1455, 1410, 1379, 1319,1262, 1238, 1223, 1161, 1015, 979, 916 cm⁻¹

¹H-NMR (600 MHz in DMSO-d₆): δ=9.23 (1H, s), 7.50 (2H, d), 7.36 (2H, d),6.73 (1H, dd), 5.86 (1H, d), 5.40 (2H, s), 5.28 (1H, d) ppm

¹⁹F-NMR (565 MHz in DMSO-d₆): δ=−73.64 (6F, s) ppm

Monomer Synthesis Example 2 Synthesis of Monomer 2

Below 20° C., 9.7 g of chloromethyl methyl ether was added dropwise to amixture of 32.8 g of Monomer 1, 16.2 g of diisopropylethylamine, and 110g of acetonitrile. The contents were stirred for 3 hours at thetemperature. After standard aqueous workup and solvent distill-off, theproduct was purified by distillation, obtaining 33.9 g (yield 91%) ofMonomer 2.

Monomer Synthesis Example 3 Synthesis of Monomer 3

Monomer 3 was synthesized by the same procedure as in Monomer SynthesisExample 2 except that Protecting agent 1 was used instead ofmethoxymethyl chloride. Yield 93%.

Monomer Synthesis Example 4 Synthesis of Monomer 4

Monomer 4 was synthesized by the same procedure as in Monomer SynthesisExample 2 except that Protecting agent 2 was used instead ofmethoxymethyl chloride. Yield 88%.

Monomer Synthesis Example 5 Synthesis of Monomer 5

Monomer 5 was synthesized by the same procedure as in Monomer SynthesisExample 2 except that Protecting agent 3 was used instead ofmethoxymethyl chloride. Yield 92%.

Monomer Synthesis Example 6 Synthesis of Monomer 6

Monomer 6 was synthesized by the same procedure as in Monomer SynthesisExample 2 except that Protecting agent 4 was used instead ofmethoxymethyl chloride. Yield 86%.

Monomer Synthesis Example 7 Synthesis of Monomer 7

Monomer 7 was synthesized by the same procedure as in Monomer SynthesisExample 2 except that Protecting agent 5 was used instead ofmethoxymethyl chloride. Yield 81%.

Monomer Synthesis Example 8 Synthesis of Monomer 8

Monomer 8 was synthesized by the same procedure as in Monomer SynthesisExample 2 except that Protecting agent 6 was used instead ofmethoxymethyl chloride. Yield 84%.

Monomer Synthesis Example 9 Synthesis of Monomer 9

Monomer 9 was synthesized by the same procedure as in Monomer SynthesisExample 1 except that a mixture of m-(chloromethyl)styrene andp-(chloromethyl)styrene was used instead of p-(chloromethyl)styrene.Yield 84%.

The product obtained at the end of purification was an isomer mixtureconsisting of major isomer (above formula) and minor isomer in a ratioof 61 mol %:39 mol %.

boiling point: 52-53° C./12 Pa

IR (D-ATR): v=3463, 3093, 3013, 1757, 1632, 1515, 1455, 1378, 1321,1262, 1238, 1223, 1162, 1017, 979, 916 cm⁻¹

¹H-NMR (600 MHz in DMSO-d₆, only major isomer): δ=9.25 (1H, s), 7.48(2H, dd), 7.37 (1H, dd), 7.28 (1H, d), 6.73 (1H, dd), 5.83 (1H, d), 5.42(2H, s), 5.29 (1H, d) ppm

¹⁹F-NMR (565 MHz in DMSO-d₆, only major isomer): δ=−73.65 (6F, s) ppm

Monomer Synthesis Example 10 Synthesis of Monomer 10

Monomer 10 was synthesized by the same procedure as in Monomer SynthesisExample 2 except that Monomer 9 was used instead of Monomer 1. Yield90%.

Adhesive Monomers 1 and 2, and PAG Monomers 1 to 5 used in the followingSynthesis Examples are identified below.

-   Adhesive Monomer 1: (2-oxo-1,3-benzoxathiol-5-yl) methacrylate-   Adhesive Monomer 2: (2-oxo-2,3-dihydrobenzoxazol-5-yl) methacrylate

-   PAG Monomer 1: triphenylsulfonium    1,1,3,3,3-pentafluoro-2-methacryloyloxypropane-1-sulfonate-   PAG Monomer 2: 5-phenyldibenzothiophenium    1,1,3,3,3-pentafluoro-2-(methacryloyloxy)propane-1-sulfonate-   PAG Monomer 3: 10-phenylphenoxathiinium    1,1,3,3,3-pentafluoro-2-(methacryloyloxy)propane-1-sulfonate-   PAG Monomer 4: 5-phenyldibenzothiophenium    1,1,3,3,3-pentafluoro-2-(3-methacryloyloxy-adamantane-1-carbonyloxy)propane-1-sulfonate-   PAG Monomer 5: 10-phenylphenoxathiinium    1,1,3,3,3-pentafluoro-2-(3-methacryloyloxy-adamantane-1-carbonyloxy)propane-1-sulfonate

Synthesis Example 1

A 2-L flask was charged with 13.4 g of Monomer 4, 16.4 g of Monomer 1,3.0 g of acenaphthylene, and 40 g of tetrahydrofuran as solvent. Thereactor was cooled to −70° C. in a nitrogen atmosphere, whereupon vacuumevacuation and nitrogen blow were repeated three times. The reactorwarmed up to room temperature whereupon 1.2 g of azobisisobutyronitrile(AIBN) was added as a polymerization initiator. The reactor was heatedat 60° C. and reaction run for 15 hours. The reaction solution wasprecipitated from 1 L of isopropyl alcohol. The white solid wascollected by filtration and dried in vacuum at 60° C., yielding a whitepolymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

Monomer 4: Monomer 1: acenaphthylene=0.30:0.50:0.20

Mw=6,800 Mw/Mn=1.88

This is designated Polymer 1.

Synthesis Example 2

A 2-L flask was charged with 12.4 g of Monomer 3, 16.4 g of Monomer 1,2.8 g of indene, and 40 g of tetrahydrofuran as solvent. The reactor wascooled to −70° C. in a nitrogen atmosphere, whereupon vacuum evacuationand nitrogen blow were repeated three times. The reactor warmed up toroom temperature whereupon 1.2 g of AIBN was added as a polymerizationinitiator. The reactor was heated at 60° C. and reaction run for 15hours. The reaction solution was precipitated from 1 L of isopropylalcohol. The white solid was collected by filtration and dissolved againin a mixture of 100 mL of methanol and 200 mL of tetrahydrofuran, towhich 10 g of triethylamine and 10 g of water were added. Deprotectionreaction of acetyl group was conducted at 70° C. for 5 hours, followedby neutralization with acetic acid. The reaction solution wasconcentrated and dissolved in 100 mL of acetone. By similarprecipitation, filtration, and drying at 60° C., a white polymer wasobtained.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

Monomer 3: Monomer 1: indene=0.30:0.50:0.20

Mw=6,100 Mw/Mn=1.59

This is designated Polymer 2.

Synthesis Example 3

A 2-L flask was charged with 14.8 g of Monomer 8, 4.9 g of4-acetoxystyrene, 2.9 g of coumarin, and 40 g of tetrahydrofuran assolvent. The reactor was cooled to −70° C. in a nitrogen atmosphere,whereupon vacuum evacuation and nitrogen blow were repeated three times.The reactor warmed up to room temperature whereupon 1.2 g of AIBN wasadded as a polymerization initiator. The reactor was heated at 60° C.and reaction run for 15 hours. The reaction solution was precipitatedfrom 1 L of isopropyl alcohol. The white solid was collected byfiltration and dissolved again in a mixture of 100 mL of methanol and200 mL of tetrahydrofuran, to which 10 g of triethylamine and 10 g ofwater were added. Deprotection reaction of acetyl group was conducted at70° C. for 5 hours, followed by neutralization with acetic acid. Thereaction solution was concentrated and dissolved in 100 mL of acetone.By similar precipitation, filtration, and drying at 60° C., a whitepolymer was obtained.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

Monomer8:4-hydroxystyrene:coumarin=0.30:0.48:0.22

Mw=8,400 Mw/Mn=1.89

This is designated Polymer 3.

Synthesis Example 4

A 2-L flask was charged with 8.2 g of3-ethyl-3-exo-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecanyl methacrylate,6.6 g of Monomer 1, 11.1 g of5-oxo-4-oxatricyclo[4.2.1.0^(3,7)]-nonan-2-yl methacrylate, and 40 g oftetrahydrofuran as solvent. The reactor was cooled to −70° C. in anitrogen atmosphere, whereupon vacuum evacuation and nitrogen blow wererepeated three times. The reactor warmed up to room temperaturewhereupon 1.2 g of AIBN was added as polymerization initiator. Thereactor was heated at 60° C. and reaction run for 15 hours. The reactionsolution was precipitated from 1 L of isopropyl alcohol. The white solidwas collected by filtration and dried in vacuum at 60° C., yielding awhite polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   3-ethyl-3-exo-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecanyl        methacrylate: Monomer 1:        5-oxo-4-oxatricyclo[4.2.1.0^(3,7)]-nonan-2-yl        methacrylate=0.30:0.20:0.50

Mw=7,500 Mw/Mn=1.83

This is designated Polymer 4.

Synthesis Example 5

A 2-L flask was charged with 8.2 g of3-ethyl-3-exo-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecanyl methacrylate,9.8 g of Monomer 1, 7.1 g of Adhesive Monomer 1, 5.6 g of PAG Monomer 1,and 40 g of tetrahydrofuran as solvent. The reactor was cooled to −70°C. in a nitrogen atmosphere, whereupon vacuum evacuation and nitrogenblow were repeated three times. The reactor warmed up to roomtemperature whereupon 1.2 g of AIBN was added as polymerizationinitiator. The reactor was heated at 60° C. and reaction run for 15hours. The reaction solution was precipitated from 1 L of isopropylalcohol. The white solid was collected by filtration and dried in vacuumat 60° C., yielding a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   3-ethyl-3-exo-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecanyl        methacrylate: Monomer 1: Adhesive Monomer 1: PAG Monomer        1=0.30:0.30:0.30:0.10

Mw=7,200 Mw/Mn=1.72

This is designated Polymer 5.

Synthesis Example 6

A 2-L flask was charged with 8.2 g of3-ethyl-3-exo-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecanyl methacrylate,13.1 g of Monomer 9, 4.4 g of Adhesive Monomer 2, 5.6 g of PAG Monomer2, and 40 g of tetrahydrofuran as solvent. The reactor was cooled to−70° C. in a nitrogen atmosphere, whereupon vacuum evacuation andnitrogen blow were repeated three times. The reactor warmed up to roomtemperature whereupon 1.2 g of AIBN was added as polymerizationinitiator. The reactor was heated at 60° C. and reaction run for 15hours. The reaction solution was precipitated from 1 L of isopropylalcohol. The white solid was collected by filtration and dried in vacuumat 60° C., yielding a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   3-ethyl-3-exo-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecanyl        methacrylate: Monomer 9: Adhesive Monomer 2: PAG Monomer        2=0.30:0.40:0.20:0.10

Mw=7,900 Mw/Mn=1.82

This is designated Polymer 6.

Synthesis Example 7

A 2-L flask was charged with 5.5 g of3-ethyl-3-exo-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecanyl methacrylate,6.4 g of Monomer 7, 5.3 g of 4-hydroxyphenyl methacrylate, 4.4 g of3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl methacrylate, 5.7 g ofPAG Monomer 3, and 40 g of tetrahydrofuran as solvent. The reactor wascooled to −70° C. in a nitrogen atmosphere, whereupon vacuum evacuationand nitrogen blow were repeated three times. The reactor warmed up toroom temperature whereupon 1.2 g of AIBN was added as polymerizationinitiator. The reactor was heated at 60° C. and reaction run for 15hours. The reaction solution was precipitated from 1 L of isopropylalcohol. The white solid was collected by filtration and dried in vacuumat 60° C., yielding a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   3-ethyl-3-exo-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecanyl        methacrylate: Monomer 7: 4-hydroxyphenyl methacrylate:        3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl methacrylate:        PAG Monomer 3=0.20:0.15:0.35:0.20:0.10

Mw=9,500 Mw/Mn=1.91

This is designated Polymer 7.

Synthesis Example 8

A 2-L flask was charged with 5.2 g of 1-(adamantan-1-yl)-1-methylethylmethacrylate, 5.6 g of Monomer 10, 5.3 g of 4-hydroxyphenylmethacrylate, 4.5 g of 3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-ylmethacrylate, 11.0 g of PAG Monomer 4, and 40 g of tetrahydrofuran assolvent. The reactor was cooled to −70° C. in a nitrogen atmosphere,whereupon vacuum evacuation and nitrogen blow were repeated three times.The reactor warmed up to room temperature whereupon 1.2 g of AIBN wasadded as polymerization initiator. The reactor was heated at 60° C. andreaction run for 15 hours. The reaction solution was precipitated from 1L of isopropyl alcohol. The white solid was collected by filtration anddried in vacuum at 60° C., yielding a white polymer.

The polymer was analyzed by ¹³C-NMR, ¹H-NMR, and GPC, with theanalytical data shown below.

Copolymer Composition (Molar Ratio)

-   -   1-(adamantan-1-yl)-1-methylethyl methacrylate: Monomer 10:        4-hydroxyphenyl methacrylate:        3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl methacrylate:        PAG Monomer 4=0.20:0.15:0.30:0.20:0.15

Mw=9,200 Mw/Mn=1.78

This is designated Polymer 8.

Comparative Synthesis Example 1

A polymer was synthesized by the same procedure as above.

Copolymer Composition (Molar Ratio)

-   -   3-ethyl-3-exo-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecanyl        methacrylate: 4-hydroxyphenyl methacrylate=0.30:0.70

Mw=9,900 Mw/Mn=1.99

This is Designated Comparative Polymer 1.

Comparative Synthesis Example 2

A polymer was synthesized by the same procedure as above.

Copolymer Composition (Molar Ratio)

-   -   4-(1,1,1,3,3,3-hexafluoro-2-methoxymethoxypropyl)styrene:        4-(1,1,1,3,3,3-hexafluoro-2-hydroxypropyl)styrene=0.30:0.70

Mw=9,700 Mw/Mn=1.79

This is designated Comparative Polymer 2.

Comparative Synthesis Example 3

A polymer was synthesized by the same procedure as above.

Copolymer Composition (Molar Ratio)

-   -   3-ethyl-3-exo-tetracyclo[4.4.0.1^(2,5).1^(7,10)]dodecanyl        methacrylate: 4-hydroxyphenyl methacrylate:        3-oxo-2,7-dioxatricyclo[4.2.1.0^(4,8)]nonan-9-yl methacrylate:        PAG Monomer 1=0.30:0.20:0.40:0.10

Mw=7,300 Mw/Mn=1.88

This is designated Comparative Polymer 3.

Examples and Comparative Examples

Positive resist compositions were prepared by dissolving each of thepolymers synthesized above and selected components in a solvent inaccordance with the recipe shown in Table 1, and filtering through afilter having a pore size of 0.2 μm. The solvent contained 100 ppm of asurfactant FC-4430 (3M Sumitomo Co., Ltd.).

The components in Table 1 are as identified below.

-   Polymers 1 to 8: polymers synthesized in Synthesis Examples 1 to 8-   Comparative Polymers 1 to 3: polymers synthesized in Comparative    Synthesis Examples 1 to 3-   Organic solvents: propylene glycol monomethyl ether acetate (PGMEA)    propylene glycol monomethyl ether (PGME) cyclohexanone (CyH)    Acid generator: PAG1 of the structural formula shown below

Basic compound: Amine 1 of the structural formula shown below

EB Writing Test

Using a coater/developer system Clean Track Mark 5 (Tokyo ElectronLtd.), the positive resist composition was spin coated onto a siliconsubstrate (diameter 6 inches, vapor primed with hexamethyldisilazane(HMDS)) and pre-baked on a hot plate at 110° C. for 60 seconds to form aresist film of 100 nm thick. Using a system HL-800D (Hitachi Ltd.) at aHV voltage of 50 kV, the resist film was exposed imagewise to EB in avacuum chamber.

Using Clean Track Mark 5, immediately after the imagewise exposure, thewafer was baked (PEB) on a hot plate at the temperature shown in Table 1for 60 seconds and puddle developed in a 2.38 wt % TMAH aqueous solutionfor 30 seconds to form a positive pattern.

Resolution is a minimum size at the exposure dose (sensitivity) thatprovides a 1:1 resolution of a 100-nm line-and-space pattern. The 100-nmline-and-space pattern was measured for line width roughness (LWR) underSEM.

The resist composition is shown in Table 1 together with the sensitivityand resolution of EB lithography.

TABLE 1 Acid Basic Organic PEB Polymer generator compound solventtemperature Sensitivity Resolution LWR (pbw) (pbw) (pbw) (pbw) (° C.)(μC/cm²) (nm) (nm) Example 1-1 Polymer 1 PAG 1 Amine 1 PGMEA(1,500) 9022.6 75 6.8 (100) (20) (1.0) CyH(200) 1-2 Polymer 2 PAG 1 Amine 1PGMEA(1,500) 80 21.4 75 7.0 (1003 (20) (1.0) CyH(200) 1-3 Polymer 3 PAG1 Amine 1 PGMEA(1,500) 90 23.3 75 7.1 (100) (20) (1.0) CyH(200) 1-4Polymer 4 PAG 1 Amine 1 PGMEA(1,500) 95 24.0 75 6.8 (100) (20) (1.0)CyH(200) 1-5 Polymer 5 — Amine 1 PGMEA(500) 95 21.3 70 4.9 (100) (0.8)CyH(1,450) PGME(50) 1-6 Polymer 6 — Amine 1 PGMEA(500) 90 21.1 70 5.2(100) (0.8) CyH(1,450) PGME(50) 1-7 Polymer 7 — Amine 1 PGMEA(500) 9020.3 70 5.1 (100) (0.8) CyH(1,450) PGME(50) 1-8 Polymer 8 — Amine 1PGMEA(500) 90 20.2 70 5.5 (100) (0.8) CyH(1,450) PGME(50) Comparative1-1 Comparative PAG 1 Amine 1 PGMEA(1,500) 90 23.5 90 8.8 ExamplePolymer 1 (12) (1.0) CyH(200) (100) 1-2 Comparative PAG 1 Amine 1PGMEA(1,500) 90 20.5 90 8.8 Polymer 2 (12) (1.0) CyH(200) (100) 1-3Comparative — Amine 1 PGMEA(500) 90 32.0 75 6.1 Polymer 3 (0.8)CyH(1,450) (100) PGME(50)

EUV Exposure Test

A positive resist composition was prepared by dissolving each of thepolymers synthesized above and selected components in a solvent inaccordance with the recipe shown in Table 2, and filtering through afilter having a pore size of 0.2 μm. The resist composition was spincoated on a silicon substrate (diameter 4 inches, HMDS vapor primed) andprebaked on a hot plate at 105° C. for 60 seconds to form a resist filmof 40 nm thick. EUV exposure was performed by dipole illumination at NA0.3.

Immediately after the exposure, the wafer was baked (PEB) on a hot platefor 60 seconds and puddle developed with a 2.38 wt % TMAH aqueoussolution for 30 seconds to form a positive pattern.

Resolution is a minimum size at the exposure dose (sensitivity) thatprovides a 1:1 resolution of a 30-nm line-and-space pattern. The 35-nmline-and-space pattern was measured for LWR under SEM.

The resist composition is shown in Table 2 together with the sensitivityand resolution of EUV lithography.

TABLE 2 Acid Basic Organic PEB Polymer generator compound solventtemperature Sensitivity Resolution LWR (pbw) (pbw) (pbw) (pbw) (° C.)(mJ/cm²) (nm) (nm) Example Polymer 7 — Amine 1 PGMEA 90 9 22 4.0 2-1(100) (0.8) (1,000) CyH(2,000) PGME(500) Comparative Comparative — Amine1 PGMEA 90 12 26 5.1 Example Polymer 3 (0.8) (1,000) 2-1 (100)CyH(2,000) PGME(500)

It is evident from Tables 1 and 2 that the resist compositions using theinventive polymers having copolymerized therein meet satisfactoryresolution, sensitivity and edge roughness. By further copolymerizing anacid generator therein, more improvements in resolution and edgeroughness are attained.

Japanese Patent Application No. 2012-271260 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A positive resist composition comprising a polymer comprisingrecurring units of the general formula (1) and having a weight averagemolecular weight of 1,000 to 500,000 as a base resin,

wherein R¹ is a straight or branched C₁-C₄ alkylene group, R² ishydrogen, C₁-C₁₅ acyl group or acid labile group, R³ is hydrogen, methylor trifluoromethyl, and a is a number in the range: 0<a≦1.0.
 2. Theresist composition of claim 1 wherein the polymer comprises recurringunits (a) and acid labile group-substituted recurring units (b1) and/or(b2) copolymerized together, as represented by the general formula (2):

wherein R¹, R² and R³ are as defined above, R⁴ and R⁶ each are hydrogenor methyl, R⁵ and R⁹ each are an acid labile group, R⁷ is a single bondor a straight or branched C₁-C₆ alkylene group, R⁸ is hydrogen,fluorine, trifluoromethyl, cyano, or straight, branched or cyclic C₁-C₆alkyl group, p is 1 or 2, q is an integer of 0 to 4, Y¹ is a singlebond, a C₁-C₁₂ linking group having an ester radical, ether radical orlactone ring, phenylene group or naphthylene group, Y² is a single bond,—C(═O)—O— or —C(═O)—NH—, a, b1 and b2 are numbers in the range: 0<a<1.0,0≦b1<1.0, 0≦b2<1.0, 0<b1+b2<1.0, and 0.1≦a+b1+b2≦1.0.
 3. The resistcomposition of claim 1 wherein the polymer further comprises recurringunits (c) having an adhesive group selected from the class consisting ofhydroxyl, carboxyl, lactone ring, carbonate, thiocarbonate, carbonyl,cyclic acetal, ether, ester, sulfonic acid ester, cyano, amide, and—O—C(═O)-G- wherein G is sulfur or NH and c is a number in the range:0<c≦0.9 and 0.2≦a+b1+b2+c≦1.0.
 4. The resist composition of claim 1wherein the polymer further comprises recurring units of at least onetype selected from sulfonium salt units (d1) to (d3) represented by thegeneral formula (3):

wherein R²⁰, R²⁴, and R²⁸ each are hydrogen or methyl, R²¹ is a singlebond, phenylene, —O—R—, or —C(═O)—Y⁰—R—, Y⁰ is oxygen or NH, R is astraight, branched or cyclic C₁-C₆ alkylene group, alkenylene orphenylene group, which may contain a carbonyl, ester, ether or hydroxylradical, R²², R²³, R²⁵, R²⁶, R²⁷, R²⁹, R³⁰, and R³¹ are eachindependently a straight, branched or cyclic C₁-C₁₂ alkyl group whichmay contain a carbonyl, ester or ether radical, or a C₆-C₁₂ aryl, C₇-C₂₀aralkyl, or thiophenyl group, Z⁰ is a single bond, methylene, ethylene,phenylene, fluorophenylene, —O—R³²—, or —C(═O)—Z¹—R³²—, Z¹ is oxygen orNH, R³² is a straight, branched or cyclic C₁-C₆ alkylene group,alkenylene or phenylene group, which may contain a carbonyl, ester,ether or hydroxyl radical, M is a non-nucleophilic counter ion, d1, d2and d3 are in the range: 0≦d1≦0.5, 0≦d2≦0.5, 0≦d3≦0.5, and0<d1+d2+d3≦0.5.
 5. The resist composition of claim 1 wherein the polymerfurther comprises recurring units of at least one type selected fromindene units (e1), acenaphthylene units (e2), chromone units (e3),coumarin units (e4), and norbornadiene units (e5), as represented by thegeneral formula (9):

wherein R¹¹⁰ to R¹¹⁴ each are hydrogen, a C₁-C₃₀ alkyl, partially orentirely halo-substituted alkyl, hydroxyl, alkoxy, alkanoyl,alkoxycarbonyl, C₆-C₁₀ aryl, halogen, or1,1,1,3,3,3-hexafluoro-2-propanol group; X⁰ is methylene, oxygen orsulfur atom; e1 to e5 are numbers in the range: 0≦e1≦0.5, 0≦e2≦0.5,0≦e3≦0.5, 0≦e4≦0.5, 0≦e5≦0.5, and 0<e1+e2+e3+e4+e5≦0.5.
 6. The resistcomposition of claim 1, further comprising an organic solvent and anacid generator, the composition being a chemically amplified resistcomposition.
 7. The resist composition of claim 6, further comprising abasic compound and/or a surfactant as an additive.
 8. A monomer havingthe general formula (4):

wherein R¹ is a straight or branched C₁-C₄ alkylene group, R² ishydrogen, C₁-C₁₅ acyl group or acid labile group, and R³ is hydrogen,methyl or trifluoromethyl.
 9. A polymer comprising recurring units ofthe general formula (1) and having a weight average molecular weight of1,000 to 500,000,

wherein R¹ is a straight or branched C₁-C₄ alkylene group, R² ishydrogen, C₁-C₁₅ acyl group or acid labile group, R³ is hydrogen, methylor trifluoromethyl, and a is a number in the range: 0<a≦1.0.
 10. Thepolymer of claim 9, comprising recurring units (a) and acid labilegroup-substituted recurring units (b1) and/or (b2) copolymerizedtogether, as represented by the general formula (2):

wherein R¹, R² and R³ are as defined above, R⁴ and R⁶ each are hydrogenor methyl, R⁵ and R⁹ each are an acid labile group, R⁷ is a single bondor a straight or branched C₁-C₆ alkylene group, R⁸ is hydrogen,fluorine, trifluoromethyl, cyano, or straight, branched or cyclic C₁-C₆alkyl group, p is 1 or 2, q is an integer of 0 to 4, Y¹ is a singlebond, a C₁-C₁₂ linking group having an ester radical, ether radical orlactone ring, phenylene group or naphthylene group, Y² is a single bond,—C(═O)—O— or —C(═O)—NH—, a, b1 and b2 are numbers in the range: 0<a<1.0,0≦b1<1.0, 0≦b2<1.0, 0<b1+b2<1.0, and 0.1≦a+b1+b2≦1.0, the polymer havinga weight average molecular weight of 1,000 to 500,000.
 11. A patternforming process comprising the steps of applying the positive resistcomposition of claim 1 onto a substrate to form a coating, baking,exposing the coating to high-energy radiation, and developing theexposed coating in a developer.
 12. The process of claim 11 wherein thehigh-energy radiation is g-line, i-line, KrF excimer laser, ArF excimerlaser, electron beam or soft X-ray having a wavelength of 3 to 15 nm.